For the purposes of weight reduction and manufacturing cost reduction, aluminum is being prevalently used instead of conventional brass for the production of heat exchangers, particularly those for automobiles. However, an aluminum-made heat exchanger is vulnerable to corrosion at its interior side which contacts with a heat exchange medium, particularly when water is contained in the heat exchange medium, and such corrosion would lead to the leakage of the heat exchange medium.
Such corrosion is attributed to the use of service water as the heat exchange medium, which service water usually contains some ions, typically such as chlorine ions, which promote the corrosion of an aluminum material.
It has been generally practised, therefore, to add a corrosion inhibitor (generally called a rust preventive) to the water-containing heat exchange medium, but the corrosion inhibitory effect of such corrosion inhibitor varies greatly depending on its concentration, and there has often been found no effect. Thus, the use of a corrosion inhibitor is not deemed as an effective measure against corrosion. Japanese Patent Publication No. 6847/71 discloses a method for forming an anti-corrosive coating on an aluminum or aluminum-alloy base, but his patent is directed to the corrosive environment as seen in beverage industries and it is not applicable to the prevention of corrosion of such a heat exchanger as a radiator for automobiles, as contemplated in this invention.